The present invention relates to a control device, for example, that constitutes a refrigerant circuit in a vehicle air conditioning apparatus, the control device controlling displacement of a variable displacement type compressor that is capable of varying the displacement based on pressure in a control chamber.
This type of control device includes a supply passage, a blood passage and a displacement control valve, for example, for a variable displacement swash plate type compressor (hereinafter a compressor). In the compressor, a crank chamber and a discharge chamber are in communication via the supply passage. The crank chamber and a suction chamber are in communication via the bleed passage. The displacement control valve adjusts an opening degree of the supply passage in accordance with cooling load. That is, controlling the displacement of the compressor is performed by a supply control.
Under the supply control, a fixed throttle is placed in the bleed passage to reduce an amount of the compressed refrigerant gas that leaks into the suction chamber through the crank chamber, namely, to prevent efficiency of a refrigerating cycle from deteriorating due to re-expansion of the leaked refrigerant gas in the suction chamber. Therefore, in a state that liquid refrigerant accumulates in the crank chamber, if the compressor, is started, the liquid refrigerant is relatively slowly discharged out of the crank chamber through the bleed passage by the fixed throttle. At the same time, a large amount of the liquid refrigerant in the crank chamber is vaporized and the pressure in the crank chamber excessively rises. Thereby, it requires relatively long time to increase the displacement of the compressor to a predetermined level after the displacement control valve closes the supply passage, in other words, starting performance of the air conditioning apparatus deteriorates.
To solve the above problem, the following structure is considered. As shown in FIGS. 8A and 8B, a crank chamber 101 and a suction chamber 102 are not only in communication via the above-mentioned bleed passage or a first bleed passage but also in communication via a second bleed passage 103. An auxiliary valve 104 is placed in the second bleed passage 103. The auxiliary valve 104 opens and closes second bleed passage 103 by moving the spool valve 104b relative to the valve seat 104a. 
Still referring to FIGS. 8A and 8B, the spool valve 104b is urged to leave the valve seat 104a by a spring 104c. The pressure in the crank chamber 101 is applied to the spool valve 104b such that the spool valve 104b leaves the valve seat 104a. The refrigerant between a displacement control valve 106 and a fixed throttle 105a in the supply passage 105 is introduced into a back pressure chamber 104d of the auxiliary valve 104. That is, a position of the spool valve 104b is determined based on a balance between urging force of the spring 104c, the force that is generated due to the pressure in the crank chamber 101 and the force that is generated due to the pressure in the back pressure chamber 104d. 
In the above constitution, if the compressor is started in a state that the liquid refrigerant accumulates in the crank chamber 101, the liquid refrigerant is vaporized. Even if the displacement control valve 106 is fully closed, the pressure in the crank chamber 101 tends to excessively rise. When the displacement control valve 106 is fully closed, on the other hand, high-pressure refrigerant in the discharge chamber 107 is not supplied to the back pressure chamber 104d of the auxiliary valve 104. Therefore, the pressure in the back pressure 104d becomes relatively small.
In this case, as shown in FIG. 8B, the spool valve 104b of the auxiliary valve 104 is left from the valve seat 104a by the urging force of the spring 104c and the second bleed passage 103 is opened. Therefore, the liquid refrigerant in the crank chamber 101 is discharged to the suction chamber 102 through the second bleed passage 103 in its vaporized state and/or its liquid state. Thus, when the displacement control valve 106 is fully closed, the pressure in the crank chamber 101 is promptly reduced. Thereby, the displacement of the compressor is promptly increased.
If the air conditioning apparatus is started and the temperature in the vehicle compartment is lowered to a predetermined temperature, the displacement control valve 106 is opened. At this time, the high-pressure refrigerant in the discharge chamber 107 is introduced into the back pressure chamber 104d of the auxiliary valve 104. Therefore, the pressure in the back pressure chamber 104d rises and, as shown in FIG. 8A, the spool valve 104b contacts the valve seat 104a against the spring 104c. Thereby, the crank chamber 101 and the suction chamber 102 are blocked. Consequently, not only an amount of the compressed refrigerant gas, which is supplied from the discharge chamber 107 to the crank chamber 101, is reduced but also an amount of the compressed refrigerant gas, which is supplied from the crank chamber 101 to the suction chamber 102, is reduced, and deterioration of efficiency refrigerating cycle is prevented.
In the above constitution, which is shown in FIGS. 8A and 8B, the auxiliary valve 104 opens and closes the second bleed passage 103 by moving the spool valve 104b relative to the valve seat 104a. Therefore, for example, if the compressor vibrates under the movement of the vehicle, the spool valve 104b that is in contact with the valve seat 104a leaves the valve seat 104a and the second blood passage 103 is opened. Thereby, controlling the displacement of the compressor is unstable.
The present invention is directed to a control device for use in a variable displacement type compressor where satisfactory starting performance of an air conditioning apparatus is compatible with stability of controlling displacement of the compressor at high level.
The present invention has a following feature. A control device controls displacement of a variable displacement type compressor for an air conditioning apparatus. The compressor has a suction pressure region, a discharge pressure region and a crank chamber in a housing. The displacement is variable according to the pressure in the crank chamber. The control devise includes a first passage, a second passage, a third passage, a displacement control valve and an auxiliary valve. The first passage is defined in the housing and communicates with the discharge pressure region. The second passage is defined in the housing and communicates with the suction pressure region. The third passage is defined in the housing and communicates with the crank chamber. The displacement control valve is placed in the first passage for adjusting an opening degree of the first passage. The auxiliary valve is placed between the suction pressure region and the crank chamber in the housing and connect the first passage and the second passage to the third passage. The auxiliary valve has a valve chamber, a spool valve and an urging means. The valve chamber is defined in the housing. The valve chamber has an inner surface. The spool valve is accommodated in the valve chamber so as to slide relative to the inner surface, on which the third passage is open. The spool valve divides the valve chamber into a first pressure chamber and a second pressure chamber, to communicate the first pressure chamber with the first passage and to communicate the second pressure chamber with the second passage. The urging means is placed in the valve chamber for urging the spool valve toward the first pressure chamber. The third passage communicates with the first pressure chamber and/or the second pressure chamber by the movement of the spool valve due to the differential pressure between the first pressure chamber and the second pressure chamber, which varies in accordance with the opening degree of the first passage.